Compositions and methods for increased ethanol production from biomass

Abstract

The present application discloses the identification of the novel K. marxianus xylose transporter genes KHT105 and RAG4, as well as the identification of a novel set of I. orientalis pentose phosphate pathway genes The present application further discloses a series of genetically modified yeast cells comprising various combinations of arabinose fermentation pathways, xylose fermentation pathways, pentose phosphate pathways, and/or xylose transporter genes, and methods of culturing these cells to produce ethanol in fermentation media containing xylose.

What is claimed is: 
     
       1. A genetically modified yeast cell that overexpresses a xylose transporter polypeptide comprising an amino acid sequence with at least 90% sequence identity to an amino acid sequence selected from the group consisting of SEQ ID NO:2 and SEQ ID NO:4. 
     
     
       2. The genetically modified yeast cell of  claim 1  further comprising an active arabinose fermentation pathway, wherein said cell comprises one or more exogenous arabinose fermentation pathway genes selected from the group consisting of AI, RK, and RE genes. 
     
     
       3. The genetically modified yeast cell of  claim 1  further comprising an active xylose fermentation pathway, wherein said cell comprises one or more exogenous xylose fermentation pathway genes selected from the group consisting of XI and XK genes. 
     
     
       4. The genetically modified yeast cell of  claim 1  further comprising an active non-oxidative pentose phosphate pathway, wherein said cell comprises one or more exogenous non-oxidative pentose phosphate pathway genes selected from the group consisting of TKL and TAL genes. 
     
     
       5. The genetically modified yeast cell of  claim 1 , wherein said cell further comprises one or more exogenous non-oxidative pentose phosphate pathways genes selected from the group consisting of RPE and RKI genes. 
     
     
       6. The genetically modified yeast cell of  claim 1 , wherein said yeast cell further comprises a deletion or disruption of one or more genes selected from the group consisting of AR/XR, arabitol 4-dehydrogenase, xylulose reductase, and XDH genes. 
     
     
       7. The genetically modified yeast cell of  claim 1 , wherein said yeast cell further comprises a deletion or disruption of one or more genes selected from the group consisting of ALD and ADH genes. 
     
     
       8. The genetically modified yeast cell of  claim 1 , wherein said yeast cell belongs to the  I. orientalis/P. fermentans  clade. 
     
     
       9. The genetically modified yeast cell of  claim 8 , wherein said yeast cell is  I. orientalis.    
     
     
       10. A fermentation process wherein a genetically modified yeast cell as recited in  claim 1  is cultured in fermentation media comprising xylose. 
     
     
       11. The fermentation process of  claim 10 , wherein said fermentation media comprises at least 10 g/L xylose from a plant biomass hydrolysate. 
     
     
       12. The fermentation process of  claim 11 , wherein xylose is the most abundant sugar in said fermentation media. 
     
     
       13. A method of producing ethanol from a xylose-containing media comprising culturing a genetically modified yeast cell as recited in  claim 1  in a xylose-containing media. 
     
     
       14. The method of  claim 13 , wherein said xylose-containing media comprises at least 10 g/L xylose from a plant biomass hydrolysate. 
     
     
       15. The method of  claim 14 , wherein xylose is the most abundant sugar in said media.